Market available consumer batteries such as button cell batteries or zinc-carbon batteries are generally called primary cell. These batteries are designed to be used once and then discarded. As primary cells are used, chemical reactions in the battery use up the chemicals, thus generating power. When the chemicals are used up, the battery stops producing electricity. Primary cells are generally cheaper to manufacture, and tend to have lower retail prices. However, the heavy metals and electrolytes contained in primary cells are harmful to the environment, resulting in environmental pollution when they are discarded. For example, if electrolytes contained in the primary cells leak out, this may cause a chemical reaction with water, which then produces toxic substances.
In recent years, research for alternatives to traditional primary cells has made significant progress. A water-activated power generating device, generally known as a water battery, is an example of the alternatives. A water battery is a battery that does not contain any electrolytes, and hence produces no voltage until it is soaked in or filled with water. Therefore, in comparison with traditional primary cells, water batteries are easily stored, since chemical reactions will not occur if no water comes into contact with the water battery. Water batteries can be stored in warehouses or on shelves for years without consuming any or the chemicals in the water battery. Furthermore, the materials used for manufacturing water batteries are environmentally friendly, which means that when a water battery is discarded, the components of the water battery can be easily recycled, and do not produce toxic substances.
However, existing water batteries have some restrictions. For example it is difficult for traditional water batteries to provide large output voltages. A traditional water battery often has a container for holding water, and the water used to fill the battery and the impurities within the water both have conductivity; therefore, a traditional water battery needs to be carefully made as an individual module with insulation, before it can be connected in series or in parallel with another water-activated power generating device.
The use of Magnesium (Mg) as the anode of a traditional water battery is one of the reasons that the life of a traditional water battery is relatively short. The Magnesium (Mg) is consumed as the water battery generates power. Due to the highly reactive properties of Mg, a fixing, component for fixing the Mg will be corroded. The chemical reactions between the Mg and the fixing component will generate heat, which then deforms the fixing component. The corrosion of the Mg in a traditional water battery will also produce a short-circuiting problem that destroys the function and decreases the life of a traditional water battery.
Therefore, there is a need to develop a water-activated power generating device that overcomes the above-mentioned problems.